title: Ethambutol induces PKC-dependent cytotoxic and antiproliferative effects on human retinal pigment cells.
abstract: Ethambutol (EMB)-induced ocular side effects may involve the influence on functions of retinal pigment epithelium (RPE), in addition to EMB-induced optic neuropathy. To address this issue, the molecular and cellular effects of EMB on RPE including growth regulation, morphological responses, phagocytic activity, and the relevant signaling pathways were investigated. EMB (at optimal concentration 8.0mM) can trigger cell cycle arrest in both RPE50 and ARPE19 cells, accompanied by reduced DNA synthesis. EMB also induced cytoplasmic vacuole formation in both RPE cell lines. Under transmission electric microscope, the phagosomes were replaced by vacuoles and the number of microvilli was reduced in EMB-treated cells. Animal experiments also demonstrated the vacuole formation within RPE of the EMB-treated rats. On the other hand, by in vitro phagocytosis assay using rod outer segment (ROS) as the target, we found EMB suppressed phagocytosis in the cultured RPE, which is consistent with the decreased rhodopsin uptake in the RPE of the EMB-treated rats. Furthermore, inhibitor of protein kinase C but not MAPK, prevented the EMB-induced phenotypical changes. Using a non-radioactive PKC assay, we also demonstrated the PKC activity in both RPE cell lines can be induced by EMB. In conclusion, EMB may exert toxic effects in RPE including suppression of cell growth, formation of cytoplasmic vacuoles and reduction of phagocytic functions via PKC signal pathway.
authors.affiliation: Department of Ophthalmology, Buddhist Tzu Chi General Hospital, Hualien, Taiwan.
authors.forename: Rong Kung
authors.initials: RK
authors.lastname: Tsai
authors.forename: Chung Hsing
authors.initials: CH
authors.lastname: Chang
authors.forename: Chi Ming
authors.initials: CM
authors.lastname: Hseu
authors.forename: Shen Ming
authors.initials: SM
authors.lastname: Chang
authors.forename: Jia-Ru
authors.initials: JR
authors.lastname: Wu
authors.forename: Hwei-Zu
authors.initials: HZ
authors.lastname: Wang
authors.forename: Wen Chen
authors.initials: WC
authors.lastname: Wu
authors.forename: Wen Sheng
authors.initials: WS
authors.lastname: Wu
mesh_terms: D000818:Animals; D000995:Antitubercular Agents / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D004247:DNA / Q000096:biosynthesis; D004977:Ethambutol / Q000494:pharmacology*; D006801:Humans; D008297:Male; D008854:Microscopy, Electron; D010587:Phagocytosis / Q000187:drug effects; D011493:Protein Kinase C / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D055213:Retinal Pigment Epithelium / Q000187:drug effects* / Q000201:enzymology / Q000648:ultrastructure; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015398:Signal Transduction / Q000187:drug effects; D014617:Vacuoles / Q000187:drug effects / Q000648:ultrastructure
chemical_list: D000995:Antitubercular Agents; D004977:Ethambutol; D004247:DNA; D011493:Protein Kinase C